Several bosses in Siege of Orgrimmar still have spell effects, on the top of my head: Gloom's electrocute cast when it lands makes a sound. Rook's melee attack make sounds. When Sun dodges it makes a sound.

And during Sha of Pride, there's a constant ambience noise going on in the room that seems to come from the Sha of Pride

Also heard several player abilities while i was doing LFR, but I couldn't pinpointed what it was, but one of them sounded like a rogue or warrior drawing/shedding his weapons..

Several bosses in Siege of Orgrimmar still have spell effects, on the top of my head: Gloom's electrocute cast when it lands makes a sound. Rook's melee attack make sounds. When Sun dodges it makes a sound.

And during Sha of Pride, there's a constant ambience noise going on in the room that seems to come from the Sha of Pride

Also heard several player abilities while i was doing LFR, but I couldn't pinpointed what it was, but one of them sounded like a rogue or warrior drawing/shedding his weapons..

sorry ,i dont know what you are discribing.but i can tell you how to find it .
1 download MPQEditor at http://www.zezula.net/mpq.html open all mpqs' sound file
2 downlad Everything1.3.3.658 seach the word like burst speed sprint.

I will try your method when I get home in the weekend.
What I am talking about is the Rogue's ability Burst of Speed, which uses the same sound as the Rogue's ability Sprint.

I'm looking to mute Burst of Speed / Sprint.
I know this AddOn mutes it somewhere in the Spells folder, but I just cannot find it!

sorry ,i dont know what you are discribing.but i can tell you how to find it .
1 download MPQEditor at http://www.zezula.net/mpq.html open all mpqs' sound file
2 downlad Everything1.3.3.658 seach the word like burst speed sprint.